1. Field of the Invention (Technical Field)
The present invention relates to sparging systems and methods of in-situ groundwater remediation for removal of contamination including dissolved chlorinated hydrocarbons and dissolved hydrocarbon petroleum products. Remediation of saturated soils may also be obtained by employment of the present invention. In particular, the present invention is directed to the use in injection wells of microfine bubble generators, matched to substrates of selected aquifer regions, for injection and distribution of said bubbles containing oxidizing gas through said aquifer. Further, the present invention relates to selectively encapsulating gases including oxygen and ozone in duo-gas bubbles which, in the presence of co-reactant substrate material acting as a catalyst, are effective to encourage biodegradation of leachate plumes which contain biodegradable organics, or Criegee decomposition of leachate plumes containing dissolved chlorinated hydrocarbons.
2. Background Prior Art
The introduction of air bubbles into aquifers for the purpose of remediation is a recent advancement in in-situ treatment of groundwater (Marley, et al., 1992; Brown et al., 1991). Contained air entrainment has been used for many years to provide vertical movement of water in low-head aquariums and in the development of public well supplies (Johnson, 1975). Aeration of aquifers for plume management was suggested to accelerate bacterial degradation of dissolved organic compounds (JRB, 1985). As bubble volume increases in density above re-aeration needs by approaching ratios beyond 1 to 10 (1 water to 10 air), gas transfer begins to dominate. In this case, volatile organics may be physically transported from the saturated aquifer to the overlying unsaturated zone (vadose zone).
There is a well-recognized need for a simple test to evaluate a potential site to assist with design of sparging systems deployed on a remediation site. Whereas hydraulic tests have been performed for some period of time based upon the well-known Theis equation, the introduction of air bubbles (particularly microscopic bubbles) is new. Also, whereas the introduction of air to the pressure vessel is continuous, the production of bubbles, particularly the microscopic variety, is a discrete discontinuous process. Bubbles, once generated, may take preferential pathways, determined largely by the substratum and, secondarily, by the introduction of pressure (Ji, et al., 1993).
Applicant is aware of prior art devices that have used injection of air to facilitate biodegradation of plumes.
U.S. Pat. No. 5,221,159 to Billings shows injection of air into aquifer regions to encourage biodegradation of leachate plumes which contain biodegradable organics together with simultaneous soil vacuum extraction.
Also in U.S. Pat. No. 4,730,672 to Payne, there is disclosed a closed-loop process for removing volatile contaminants. However, Payne deals only with volatile contaminants. Payne discloses a withdrawal well surrounded by multiple injection wells. Pressurized air is injected into the groundwater through the injection wells, and is withdrawn under vacuum from the withdrawal well whereupon contaminants are removed from the air stream and the air is then recycled through the system. The U.S. Pat. No. 4,588,506, to Raymond et al. discloses the injection of a diluted solution of hydrogen peroxide into a contaminated soil for enhancing biodegradation of organic contaminants in the soil. Raymond discloses intermittent spiking of the hydrogen peroxide concentration to eliminate biota to increase soil permeability. Raymond has the disadvantage of failing to deliver oxygen through the system, and depends on a complicated process of hydrologic management of the subsurface which has rendered the process uneconomical.
In U.S. Pat. No. 5,167,806 to Wang et al. there is disclosed apparatus for treatment of a contaminated liquid stream comprising generating extremely fine gas bubbles through porous diffusers, wherein the gas may be a combination of air and ozone. One process disclosed by Wang involves removing dissolved organics from contaminated groundwater by means of generating micro gas bubbles. In the first stage of the process for removing dissolved organics, which involves generating bubbles, no vacuum is employed, as gas bubbles are completely dissolved by the method. Wang teaches an enhanced dissolved aqueous reaction.
In U.S. Pat. No. 4,832,122 to Corey et al. is disclosed an in-situ method for removing contamination from groundwater comprising a horizontal well positioned in the saturated zone which has multiple apertures for injecting gas. The apertures are shown in the figures to be sequentially arranged and closely spaced so that the bubbles zones produced from each one would overlap with the adjacent zones. Corey et al. teaches that the configuration of the injection system is dictated by the size and shape of the plume, drilling economics, and the subsurface geology (column 1, lines 4–9, 41–43, 64–68; column 2, lines 1–8, 43–48). Corey also teaches an enhanced dissolved aqueous reaction.
U.S. Pat. No. 4,614,596 to Wyness discloses a method for dissolving a gas in an aqueous stream which comprises diffusing a gas in an aqueous stream to produce small gas bubbles which are rotated to provide a long flow distance over which the bubbles have increased contact time. The figures show that the bubbles are dispersed within and outward from a vessel, or well casing, by maximizing the dispersal of bubbles from a well casing and maximizing contact with the bubbles. Wyness also teaches an enhanced dissolved aqueous reaction.
Notwithstanding the teachings of Wang et al., Corey et al., and Wyness, there has not been shown a sparging system for remediating a site in a controlled manner of poorly biodegradable organics, employing oxidizing gas encapsulated in microbubbles generated from microporous diffusers matched to soil porosity pulsed in a wave form for even distribution through the substrate (aquifer structure) employing a co-reactant in the form of substrate material. Further, the prior art fails to show matching of micron sized bubble formation with substrate material of a selected aquifer or to show the beneficial effect of uniform distribution of sized bubbles through such a formation by means of a pulsed wave form without fracturing said substrate. The present invention accomplishes this by injecting micron size bubbles into aquifer regions in combination with substrate materials acting as a catalyst to encourage biodegradation of leachate plumes which contain biodegradable organics by means of a gas/gas/water reaction which overcomes at least some of the disadvantages of prior art.